Two main families of polyunsaturated fatty acids (PUFAs) are the omega-3 fatty acids such as eicosapentaenoic acid (EPA) and the omega-6 fatty acids such as arachidonic acid (ARA; cis-5, 8, 11, 14-eicosatetraenoic). ARA is an important precursor in the production of eicosanoids (e.g., prostaglandins, thromboxanes, prostacyclin and leukotrienes). Additionally, ARA is recognized as: (1) an essential long-chain polyunsaturated fatty acid (PUFA); (2) the principal omega-6 fatty acid found in the human brain; and, (3) an important component of breast milk and many infant formulas, based on its role in early neurological and visual development.
Adults obtain ARA readily from foods such as meat, eggs and milk. Adults also can synthesize ARA from dietary gamma-linolenic acid albeit inefficiently. Commercial sources of ARA oil are typically produced from highly refined and purified fish oil or fermentation (e.g., using microorganisms in the genera Mortierella (filamentous fungus), Entomophthora, Pythium and Porphyridium (red alga)). Most notably, Martek Biosciences Corporation (Columbia, Md.) produces an ARA-containing fungal oil (ARASCO®; see U.S. Pat. No. 5,658,767) which is substantially free of EPA and which is derived from either Mortierella alpine or Pythium insidiuosum. One of the primary markets for this oil is infant formula.
Unfortunately, there are several disadvantages associated with commercial production of PUFAs (such as ARA) from natural sources. Natural sources of PUFAs, such as fish, tend to have highly heterogeneous oil compositions. The oils obtained from these sources can require extensive purification to separate out one or more desired PUFAs or to produce an oil which is enriched in one or more PUFAs. Natural sources also are subject to uncontrollable fluctuations in availability. Fish stocks may undergo natural variation or may be depleted by overfishing. Fish oils have unpleasant tastes and odors which may be difficult, if not impossible, to economically separate from the desired product and can render such products unacceptable as food supplements. Animal oils and, in particular, fish oils, can accumulate environmental pollutants. Weather and disease can cause fluctuation in yields from both fish and plant sources.
An expansive supply of ARA from fish and from chemical synthesis are not sufficient for commercial needs. Therefore, it is of interest to find alternative means to allow production of commercial quantities of ARA. Biotechnology using an oilseed plant offers an attractive route for producing ARA in a safe and cost efficient manner.
Applicants' Assignee's co-pending application include the following: (1) PCT Publication No. WO 04/071467 (published Aug. 26, 2004) concerns the production of PUFAs in plants; (2) PCT Publication No. WO 04/071178 (published Aug. 26, 2004) concerns annexin promoters and their use in expression of transgenes in plants; (3) PCT Publication No. WO 05/047479 (published May 26, 2005) discloses a delta-15 desaturase from Fusarium moniliforme; (4) U.S. application Ser. No. 11/601,563 (filed Nov. 16, 2006, which published May 24, 2007) discloses a delta-9 elongase from Eulgena gracilis; (5) U.S. patent application Ser. No. 11/737,772 (filed Apr. 20, 2007) discloses a delta-8 desaturase from Pavlova lutheri; (6) U.S. patent application Ser. No. 11/748,629 (filed May 15, 2007, which published Dec. 20, 2007) discloses a delta-5 desaturase from Eulgena gracilis; and (7) U.S. patent application Ser. No. 11/876,115 (filed Oct. 22, 2007) discloses a delta-8 desaturase from Tetruetreptia pomquetensis CCMP1491.